J. F. Bunnett and B. F. Hrutfiord, J. Am. Chem. Soc., vol. 83, pp. 1691-1697 (1961) report that orthohalo substituted anilides, in contact with potassium amide in liquid ammonia, form benzoxazoles. It is postulated that the active intermediate has a negative charge on the amido oxygen. No polymers are used or mentioned in this paper.
M. I. El-Sheikh, et. al., J. Org. Chem., vol. 46. pg. 3256-3259 (1981), report results similar to those of Bunnett, supra, but report the product is formed via an o-hydroxyphenyl amidine, which is thermally unstable and on heating gives the benzoxazole. Again, no polymers are used or mentioned.
E. M. Pearce and coworkers in a series of papers (J. Polym. Sci., Polym. Chem. Ed., vol. 22, pg. 3999-4009 (1984); J. Polym. Sci., Polym. Chem. Ed., vol. 19, pg. 2835-2840 (1981); J. Polym. Sci., Polym. Chem. Ed., vol. 22, pg. 847-850 (1984); J. Polym. Sci., Part A, vol. 25, pg. 171-180 (1987); J. Polym. Sci., Polym. Chem. Ed., vol. 22, pg. 3989-3998 (1984); all of which are hereby included by reference) report the thermal decomposition of halogenated aromatic polyamides. When the halogen atom is ortho to the nitrogen atom of the amide, benzoxazoles are shown to be formed. This reaction is strictly thermal, and occurs during decomposition of the polymer, so is difficult to control and of little use for synthetic purposes.
A similar thermal reaction is reported in Japanese Patent 70018875, by heating certain aromatic polyamides in vacuum or under a stream of ammonia.
Another thermal reaction to produce polybenzoxazoles is reported in Japanese Patent 71012745. Halogenated polyamides are heated at 50.degree.-400.degree. C., preferably 200.degree.-400.degree. C., optionally in the presence of a dehydrating agent, to produce the benzoxazole. A similar process is reported in Japanese Patent 71012476.
Polyamide anions are known in the art, for example see M. Takayanagi and T. Katayose, J. Polym. Sci., Polym. Chem Ed., vol. 19, pg. 1133-1145 (1981); M. Takayanagi and T. Katayose, J. Polym. Sci., Polym. Chem. Ed., vol. 21, pg. 31-39 (1983); R.R. Burch, et.al., Macromolecules, vol. 23, pg. 1065-1072 (1990); and U.S. Pat. Nos. 4,785,038 and 4,824,881. None of these references suggests the synthesis of ortho-halo substituted aromatic amides, or any uses for such compounds.
It is the purpose of the present invention to provide a simple, controllable and high yield method for the conversion of halogenated polyamides to benzoxazoles. To accomplish this, novel halogenated polyamide anions are provided.